Proteins have been widely used as ingredients in personal care products, pigment coating, and in bandages to promote wound healing. Use of silk proteins to perform a variety of functions and to impart desired characteristics to product formulations has been described (See e.g., U.S. Pat. No. 5,747,015; Japanese Patent No. 27186; and Japanese Patent No. 309816). In these disclosures, silk protein hydrolysates were used because of the low solubility of intact silk proteins. For example, for these reasons, proteins have been used to impart some beneficial coating effects such as manageability and strength to hair, to moisturize skin and hair, and to provide film formation to improve the appearance of skin and hair. Proteins have also been used to provide durability properties to many personal care products.
However, such proteins may not exhibit all desired characteristics when used in personal care products. For example, natural silk proteins may impart durability but may also form tight, hard fibers that are not suitable for film formation. Also, many natural proteins have a low isoelectric point, which reduces the affinity of the protein for the negatively charged skin and hair. Additionally, when more than one protein is needed to impart all desired characteristics to a given formulation, the necessity of using more than one protein may increase the cost and production time for a given personal care product.
Furthermore, proteins generally have poor solubility due to high molecular weight and hydrophobicity. Commercially available proteins, including structural proteins such as silk and collagen, are typically chemically degraded giving a diverse mixture of molecular weight fragments with variable properties (See e.g., German Patent No. 3139438; and U.S. Pat. No. 6,280,747). However, in most embodiments, hydrolyzed proteins have not been found to be as effective as the intact proteins, as the beneficial effects of the self-assembly, nanofibrilation and coating properties have not realized. As such, these proteins are often modified chemically (See e.g. U.S. Pat. No. 6,296,860) to enhance solubility for inclusion in personal care products and coating pigments for personal care use (See e.g. U.S. Pat. No. 4,325,741). However, even chemically modified proteins may not have all desired characteristics.
In addition, in the wound care area, enzymatically digested silk protein has been described as being useful as a healing promoter in wound dressings (See e.g. U.S. Pat. No. 5,382,431). However, digested silk protein is not as effective as water-soluble silk protein (See e.g., WO 04/044172). U.S. Pat. No. 6,175,053 describes the use of dissolved silk proteins as a wound dressing material. However, these preparations required harsh solvents to dissolve the silk protein prior to use.
Thus, there remains a need in the art for personal care compositions that have desired characteristics without undesirable chemical modification of the proteins. There also remains a need in the art for a method of delivering a protein into a personal care composition so as to effectively deliver the protein in a useable form.